Otitis media with effusions (OME), or serous otitis media, is a common condition in children and frequently leads to deafness at a critical age of development. The broad objective of this research is to study OME in order to elucidate the pathogenesis of this condition. The immediate goals of this study are: 1) to clarify the role of subclinical infection in OME pathogenesis, 2) to clarify the role of immune response in the formation of effusions, 3) to devise practical diagnostic laboratory procedures (if the pathogeneses are established), and 4) to develop an animal model of OME to test the following hypotheses: a. Many cases of OME are low-grade infections modified by the bacteriostatic substances in the effusion, and the organisms develop a tolerance to these substances. b. Inadequate antibiotic treatment of an initial ear infection prevents the development of adequate immunity of the ear, particularly in the young age group, whose immune systems are being developed, and subsequent infection results in OME. c. Initial infection may sensitize the middle ear mucosa and tubal epithelium. Subsequent infection may result in a middle ear effusion caused by immune response.